1. Field of the Invention
This invention relates to methods of preparing frozen comestibles for immediate consumption.
2. Brief Statement on the Prior Art
Frozen convenience foods have made very successful inroads in the consumer marketplace. However, such frozen foods typically require long periods of time to heat viz., up to an hour and more, in conventional particularly those with large amounts of a frozen sauce primarily of water, fats, spices, thickeners and binders).
Certain prior art allow for more efficient heat exchange via an enclosure for the frozen convenience food, e.g., the so-called "boil-in-bag" for immersion in boiling water. The boil-in-bag technique obviates the need for a conventional oven, which heats primarily by radiation. It also is an efficient means of heat exchange, since the air in the interior of the bag is heated and the heated air evenly heats the frozen comestible therein. By using this heating source, relatively prompt heating occurs, and, unlike a conventional oven, the heated air is moist and will not tend to dehydrate the comestible as much as a conventional oven would, where such dehydration is undesirable. However, these boil-in-bag devices still suffer from drawbacks, such as the need to boil the water beforehand and a still considerable amount of cooking time. There is also a danger of dehydrating part of the comestible, or achieving inconsistent cooking times because of the differences in density of the materials cooked therein. One partial attempt to solve this latter problem was disclosed in Tressler, U.S. Pat. No. 3,567,468. Tressler disclosed individually quick frozen constituents which were combined with a dry sauce mix, all contained in a boil-in-bag. The dry sauce mix becomes hydrated upon heating the boil-in-bag by the residual moisture of the constituents of the comestible, e.g., the vegetables. Unfortunately, this technique still does not avoid the prior step of boiling water and requires monitoring so that the contents are not overcooked. Additionally, the amount of water or other liquid present in the comestible may not be sufficient to produce a desirable amount of sauce or coating, and more water may need to be initially added to the comestible, which basically adds another frozen mass which needs to be thawed during cooking, thereby increasing the heating time.
In a further step towards added consumer convenience, the microwave oven was introduced in the 1940's. Today, the number of microwave ovens in domestic use has been estimated at over 60% of all U.S. households and an even greater number in commercial use. Microwave ovens function by emitting radiation at a frequency (300 to 3,000 Megahertz, and, most preferably, 915 to 2,450 Megahertz) below that of visible light. When microwave radiation impinges a material, depending on whether the material transmits, absorbs, or reflects such radiation, the material may allow such radiation to pass through, may be heated or may redirect or intensify such radiation. Materials, such as glass, ice or certain plastics, allow microwave radiation to pass through with minimal or no absorption. Other materials, such as most metals, reflect microwave radiation. However, most foods containing moisture absorb, and thus, are heated by, microwave radiation. Briefly, microwave radiation acts as an applied electric field which causes the dipoles in water to orient themselves in a certain fashion along such electric field, thereby storing potential energy. Upon oscillation of the field, the dipoles attain a new equilibrium position, and the energy is released as kinetic energy (heat). Taking advantage of these unique properties of microwave radiation on foods, some companies have developed innovative products, such as The Clorox Company in Hsia et al, U.S. Pat. No. 4,518,618, which discloses microwaveable coating mixes, yielding crisp food coatings for a variety of food substrates; and The Pillsbury Company, with specialty microwaveable containers containing a metallized "susceptor" to crisp dough on products such as frozen pizza.
Thus, microwaveable frozen comestibles must be specialty-packaged. The material must be transparent to microwave radiation. However, because microwave heating involves heat generated internally in the frozen comestible, moisture losses due to evaporation can be just as severe as in conventional oven heating. Moreover, unevenly sized food constituents can lead to uneven heating, e.g., overheating as to some portions, underheating as to others, or a combination of these. This is because microwave radiation only penetrates to a certain depth of the food until energy is fully absorbed. The rest of the interior is heated by heat conduction only. Also, because most frozen food products contain premade sauce, and the sauce is constituted of some edible liquid, more problems can be observed. The sauce must be specially constituted to prevent separation into watery and solid phases. Most importantly, the relatively large amount of water or liquid in such sauces signifies longer exposure to microwave radiation is necessary to generate sufficient heat to melt the ice by conduction. This again leads to uneven heating.
One attempt to circumvent the problem of uneven heating is a recent introduction by General Foods Corporation under the brand name "Bird's-Eye Fresh Creations" frozen dinners. These products borrow on the boil-in-bag concept by separately pouching each of the main constituents in e.g., an entree, for separate microwave heating of each. This approach, however, suffers from the complexity of the heating sequence (each separate constituent requires different heating times, different preparation, or both).